Soft type and hard type contact lenses have conventionally been used for the purpose of vision corrections of myopia, hyperopia, astigmatism and presbyopia and the like.
Since these contact lenses are worn over the sensitive corneal surface, it is required to achieve a comfortable wearing sensation by alleviating the foreign-body sensation. In order to enhance the wearing sensation, one can consider adopting a double-thin type lens with its upper and lower sides made thinner than the left and right sides in the peripheral zone located along the peripheral part of the optical zone. Thinning the upper and lower sides makes it possible to reduce the pressure from the eyelids and restrict the foreign-body sensation. Also, since taking advantage of the action of interference with the eyelids can prevent the contact lens during wear from turning around, such can be favorably applied to tonic lenses and the like. See Patent Document 1 (Japanese Publication of PCT International application No. JP-A-2007-503017) and Patent Document 2 (Japanese Patent Publication No. JP-A-2000-89172), for example.
However, in case of a double-thin type contact lens, there was a problem of hardly being able to maintain enough oxygen permeability and tear exchange. In other words, in case of a double-thin type contact lens, the left and right sides in the peripheral zone are made relatively thick so that the oxygen permeability tends to drop down. Moreover, since the amount of lens displacement over the corneal surface caused by blinking tends to get smaller to reduce the tear exchange by making the upper and lower sides in the peripheral zone so thin as to get under the eyelids, supply of oxygen to the cornea due to tear exchange tends to be lower. In addition, because of the reduced tear exchange, there was a problem of difficulties in removing the impurities including waste materials such as lactic acid and dead epithelial cells as well as bacteria and the like, for example, generated by corneal metabolism, or even air bubbles trapped between the cornea and the lens during wear and so forth.